7 replies to this topic

[Martin Belair]

Some people are certain that the new four strokes are going to be a great addition to our sport. Some people are sure that it will mean the end of the world. Some people are wondering about the advantages that the four stoke will offer the trials rider.

While it is true that we won't know for certain how they will perform until they get here, I found this description of four stroke power, written by Cycle World's Technical Editor Kevin Cameron, very interesting.

"The major advantage of the four stroke is that its power, as the throttle is initially opened, begins near zero and increases smoothly, especially in mildly tuned engines with short cam timing. In the two stroke this is not possible, because at low throttle, fresh charge is so diluted by exhaust gas left from the previous cycle that it cannot at first be ignited. When it fires, (two-stroke) it does so only after several cycles have delivered enough charge to be ignited. Torque therefore increases in chunks, as eight-stroking becomes four-stroking, and four-stroking jumps to steady firing-torque doubling at each step. Devices such as exhaust power-valves have helped, but this problem has never gone away. Therefore a rider on a four-stroke can safely send power to the rear tire sooner, and so begin acceleration earlier."

Kevin Cameron - Technical Editor Cycle World Magazine - February 2003

[t-shock 250]

I don't think that actually applies to trials engines in practice, you can't get much more controllable power than a trials 2 stroke.

[Gaff]

Had my first trial on a 4-stroke (87 RTL) over Christmas, and although i could not help but compare to my modern mount, (as in weight and responce) i just loved the way the power seems to come from nowhere, extra traction and the way it just stops on the spot when you close the throttle quick. All i need to sort-out/master is that flaming "spit-back".
Gaff.

[Marky G]

Gaff, on Jan 9 2004, 12:03 AM, said:

Had my first trial on a 4-stroke (87 RTL) over Christmas, and although i could not help but compare to my modern mount, (as in weight and responce) i just loved the way the power seems to come from nowhere, extra traction and the way it just stops on the spot when you close the throttle quick. All i need to sort-out/master is that flaming "spit-back".
Gaff.

Fourstrokes seem to spit back or pop and cut out allot, I've had a couple of TLR's in the past and both of them did it!.

My Kawasaki KLX650 does it, and it can be a pig to start once it has 'popped out'.

Antbody know how to stop this 4stroke trait??


Gaff,
You must have won the lotto buying an RTL The prices of the old Honda fourstrokes has gone through the roof lately, there's a TLR 250 in TMX and the guys asking over 2k for it!!.

I'm waiting for a bigger version of the Scorpa 125 before I make my mind up.


Mark

[mattylad]

As a confirmed 2 stroke man I rode the 125 Scorpa last week . What an amazing little bike very user friendly engine. Bit down on power but really an eye opener. I cant wait for the bigger bikes. If only I could get ny Cub to go like it.

[HRC2002]

Will the four stroke be cheaper?

[Eric23]

While waiting for my Yamaha trials bike to be rebuilt, I've spent the last couple of months riding my Kawasaki KLX300 on singletrack enduro trails in the deserts of Arizona. The low end torque is amazing. I can find traction (sometimes too much) without losing the powerband. Although the engine braking is fine for trail/fun riding I can see where it would be a liabilty for trials work. You do feel the added weight at the end of the day, but the KLX carries it low, as would a properly designed trials frame. I'd like to test a modern 4 stroke trials machine. I've ridden a couple of vintage Hondas and the engine braking was too severe for my taste in the sections. However on the trails, thumpers are a blast.

[mark christopher]

HRC2002, on Jan 13 2004, 04:22 PM, said:

Will the four stroke be cheaper?

an not see them being cheaper someone has to pay for the development!